Radioactive strontium containment



United States Patent 3,161,600 RADIOACTIVE STRONTIUM CONTAINMENT Gerald B. Barton, Kennewick, Wasln, assignor to the United States of America as represented by the United States Atomic Energy Commission N0 Drawing. Filed Dec. 18, 1962, Ser. No. 245,949 Claims. (Cl. 252-3011) The invention relates to a novel composition and method of containing radioactive strontium, more particularly to its containment within a nonflammable, highly insoluble material from which it may later be conveniently extracted, thereby making it suitable for ordinary shipping operations.

Strontium-90 has many useful applications in industrial, medical and food-processing irradiations, in leak testing and thickness testing; and as a heat source for thermoelectric devices. However, it is highly dangerous and care must be taken to prevent even trace amounts from escaping since these can create a public health hazard. Containers have an inherent risk of failure no matter how carefully made, and for this reason it is known to encapsulate radioactive strontium in organic plastics, or inorganic materials such as metals, cement and glass. The above inorganic materials have the advantages of being nonflammable and resistant to the solvent action of water and organic liquids, so that accidental wetting by either of these constitutes no great hazard. These materials are disadvantageous, in that once the radioactive material is placed within them it is difliicult to extract. Any such extraction requires that the cement or glass be finely ground or otherwise comminuted, and this creates a problem of radioactive dust which militates against the use of inorganic materials for encapsulating strontium-9O in ordinary shipping operations where the consignee normally needs to have the radioactive material in soluble form before he can process it further.

It is, accordingly, the general object of the invention to provide a method of containing radioactive strontium within a non-flammable, highly insoluble material from which it can be readily extracted.

It is a more particular object to provide a method of handling Sr in ordinary shipping operations so as to avoid the hazards due to accidental wetting by water or organic liquids and those of radioactive dust resulting from fine comminuting.

According to the invention, radioactive strontium as strontium oxide is made one of the two main constituents of a glass composition, the other main constituent being phosphorous pentoxide, and with, optionally, minor amounts selected from members of the class consisting of SiO B 0 A1 0 MgO and Na O. This results in a glass thatis highly resistant to the solvent action of water, even at boiling temperature, and yet it is readily dissolved in strong acid, such as strong HNO The components above mentioned as being present in minor amounts are often present merely as impurities. They may also be added intentionally to control recrystallization and hence the glassiness of the product. In their absence there is more of a tendency for cracks to develop on cooling. They are therefore desirable, but not essential to the invention.

The proportions of the glass composition may be varied within certain ranges for each constituent; raising the P 0 content, in general, lowers the melting point, which is advantageous in certain respects, and raising the SrO content, while raising the melting point, also decreases water solubility and acid solubility, which is desirable when extraction of the strontium content is not contemplated. In any case, the operable range, in weight percentages, of the major constituents of the glass in ques- 3,161,600 Patented Dec. 15, 1964 ice tion is as follows: 30 to 60 w/o SrO, 33 to 65 w/o P 0 Since it is desirable in most applications that the glass have glassiness and be free from cracks, it is preferable in such cases that the minor constituents be present in the following weight percentages: 1 to 2% W/o SiO 2 /2 to 4 /2 w/o B O /2 to 1 w/o A1 0 .50 to .75 w/o MgO and, when selected, 02.5O w/o Na O. It will be understood that for practical purposes the strontium in the SrO is radioactive, so that the composition may also be written to include Sr O.

For most purposes my preferred proportions are 58.2 W/o SrO, 33.1 w/o P 0 2.34 w/o SiO 4.54 w/o B 0 0.95 w/o A1 0 and 0.81 w/o MgO, it again being under stood that the first ingredient may be mainly Sr O. This glass has a pouring temperature of 1350 C. and a solubility in boiling water of only 0.03 percent, as determined by immersion tests of buttons weighing 6.9 grams immersed in boiling water for four hours, the buttons being weighed before and after the immersion period.

For applications where a slightly greater water solubility can be tolerated several other compositions have been found satisfactory, and these, together with my preferred composition are set forth in Table I below, each vertical column having data pertaining to the same composition:

TABLE I Composition of Phosphate Glasses [Weight percent (calculated from weighed salts)] 1. 1 Slight Slight 1 Solubility based on holding 6.9 button of sample in 200 ml. boiling water for 4 hours.

2 Visual observation showed little attack on sharp edges.

All the glass compositions shown in the above Table I are easily soluble in boiling strong acids, such as 7.9 N nitric acid. Comparatively massive pieces, up to 6.3 grams dissolve completely in the acid mentioned in all cases within four hours, and usually within fifteen minutes or so, even without any stirring.

From the foregoing it is apparent that I have discovered an efficient means for containing Sr and one for handling it in ordinary shipping operations. Large amounts of Sr up to about 60 percent SrO, may be incorporated in the glass which holds it tightly and with extreme resistance to leaching by water, in case of accidental wetting. The glass, of course, also has complete resistance to leaching by organic liquids and solvents, since it is a true inorganic glass. Hence my compositions provide a convenient means for shipping radioactive strontium with a higher degree of physical dependability than any mechanical container could ever attain, and with great resistance to leaching should it accidentally come into contact with water. Yet when the glass is received by the consignee he will be able to extract the strontium very easily, simply by placing the glass in strong acid, such as nitric acid above mentioned. No dangerous dust-creating operation such as grinding will be required, in order that the consignee may recover the strontium in a usable form for whatever processing he has in mind.

In carrying out the invention, it is theoretically possible to blend the oxides of the final glass composition and melt them together. However, for practical reasons it is preferable to. mix stoichiometric amounts of precursor materials which are converted to the oxides mentioned in the glass furnace. For SrO my preferred precursor is Sr(NO for MgO it is Mg(NO -6H O, for B it is H BO for A1 0 it is Al(NO -9H O, for SiO it is colloidal silica sol, and for P 0 it is aqueous H PO For Sr O the preferred precursor is Sr (NO With the exception of the colloidal silica sol these may all be dissolved together in water to form a common solution, and the colloidal silica sol may be suspended in the solution, thus insuring a much more uniform admixture than it the oxides of the final compositions were blended together. The resulting suspension should then be evaporated to dryness and the resulting cake of solids pulverized and blended in order to overcome any Stratification that may have occurred during the drying step. The pulverized powder may then be transferred to a suitable container and put in the glass melting furnace. The resulting melt may be cast into convenient shapes of any kind, such as buttons. Annealing is normally not necessary for the purposes of this invention, although special situations may be found later where it would be advisable.

EXAMPLE I 40.57 g. of Sr(NO 1.75 g. of Mg(NO -6H O, 2.75 g. of H BO 2.40 g. of Al(NO -9H O, 2.15 ml. of Ludox, a colloidal silica sol, and 23.87 ml. of 6.67 M H PO were dissolved in 200 ml. of water in a beaker. These were stirred together until the suspension of silica sol was uniform in the solution, and the beaker was put on a hot plate underneath a heat lamp until the suspension was evaporated to dryness. The cake of solids re maining in the beaker was transferred to a mortar where it was ground to a fine powder, which was then transferred to a platinum crucible, which was placed in a muflie furnace with an atmosphere of air. The temperature of the furnace was raised to about 1350 C. for a total heating time of about 4 hours.

The crucible was withdrawn from the furnace and the melt within it was cast, without annealing, into buttons of approximately 6.9 grams and one of 4.1 grams. The buttons, on cooling, were weighed and immersed in 200 ml. boiling water for 4 hours, removed, dried, and reweighed. From their loss of weight their boiling-water solubility was recorded and found to be 0.03%.

The 6.9 gram buttons were then immersed in 200 ml. of boiling 7.9 N HNO for four hours. At the end of the period all the 6.9 gram buttons had dissolved completely.

The 4.1 gram button was then placed in 200 ml. of boiling 7.9 N HNO and kept under visual observation. At the end of 15 minutes it had dissolved completely.

EXAMPLES II, III AND IV 3)2, 3)2 a)2' 2 2 3 Al(NO Ludox, 6.67 M H PO and Na CO and water were mixed in three separate beakers in such proportions that when evaporated to dryness and fired under oxidizing conditions in accordance with the procedure of Example I the respective temperatures indicated in the table and Table I were obtained. The three glasses were poured at the respective temperatures indicated in the table and exhibited the respective solubilities indicated in the table.

These glasses were all found to be readily soluble in boiling 7.9 N HNO It will be understood that the invention is not limited to the details given herein but that it may be modified in accordance with the appended claims.

What is claimed is:

1. A glass composition consisting essentially of from about 30 to about weight percent Sr O and from about 33 to about weight percent P 0 2. A glass composition consisting essentially of about 30 to 60 weight percent SrO, about 33 to 65 weight percent P 0 about zero to 2 /2 weight percent SiO about zero to 4 /2 weight percent B 0 about zero to 1 weight percent Al O about zero to 4 weight percent MgO and zero to about 2 /2 weight percent Na O, a portion of the strontium of the SrO being the radioisotope Sr 3. A glass composition consisting essentially of about 30 to 60 weight percent SrO, about 33 to 65 weight percent P 0 about 1 to 2 /2 weight percent SiO about 2 /2 to 4 /2 weight percent B 0 about /2 to 1 weight percent A1 0 about /2 to weight percent MgO and zero to about 2 /2 weight percent Na O, a portion of the strontium of the SrO being radioisotope Sr 4. A glass composition consisting essentially of about 30 to 60 weight percent SrO, a portion of the strontium of said SrO being the radioisotope Sr about 33 to 65 weight percent P 0 and minor amounts selected from members of the class consisting of SiO B 0 A1 0 MgO and Na 0, the said SiO being present in the amount of about 1 to 2 weight percent, the said B 0 being present in an amount of about 2 /2 to 4 /2 weight percent, the said A1 0 being present in an amount of about /2 to 1 weight percent, the said MgO being present in an amount of about /2 to weight percent and the said Na O being present when so selected in an amount up to 2 /2 weight percent.

5. A glass composition consisting essentially of about 58.2 weight percent Sr O, about 33.1 weight percent P 0 about 2.35 weight percent SiO about 4.54 weight percent B 0 about 0.95 weight percent A1 0 and about 0.81 weight percent MgO.

References Cited by the Examiner Grover et al.: Atom, vol. 56, June 1961, pp. 18, 19 and 21 (Tk 9001.A6).

C & E'News, Dec. 11, 1961, pages 62-64. TP 1 I418.

CARL D. QUARFORTH, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,161,600 December 15, 1964 Gerald B. Barton It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 6, after "Al O insert a comma; line 12,

2 3 for "2.34" read 2.35 same column 2, Table 1, columns 4 and 5, lines 8 and 9 thereof, for

"1,025 and "825 read 1,025 and 8Z5 Slight Slight Slight Slight column 4, line 2, strike out "temperatures indicated in the table and" and insert instead glasses listed in Columns 2, 3, and 4 of Signed and sealed this 15th day of June 1965. (SEAL) Attest:

ERNEST W. SWIDER I EDWARD J. BRENNER Aitesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,161,600 December 15, 1964 Gerald B. Barton It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 6, after "A1 0 insert a comma; line 12,

2 3 for "2.34" read 2.55 same column 2, Table I, columns 4 and 5, lines 8 and 9 thereof, for

"1,025 and "825 read 1,025 and 825 Slight Slight Slight Slight column 4, line 2, strike out "temperatures indicated in the table and" and insert instead glasses listed in Columns 2,. 3, and 4 a i Signed and sealed this 15th day of June 1965. (SEAL) Attcst:

ERNEST W. SWIDER a EDWARD J. BRENNER Aitcsting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,161,600 December 15, 1964 Gerald B. Barton It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 6, after "Al O insert a comma; line 12,

2 3 for "2.34" read 2.35 same column 2, Table I, columns 4 and 5, lines 8 and 9 thereof, for

"1,025 and "825 read 1,025 and 825 Slight Slight Slight Slight column 4, line 2, strike out "temperatures indicated in the tabl and" and insert instead glasses listed in Columns 2,. 3, and 4 o Signed and sealed this 15th day of June 1965. (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER.

Altosting Officer Commissioner of Patents 

1. A GLASS COMPOSITION CONSISTING ESSENTIALLY OF FROM ABOUT 30 TO ABOUT 60 WEIGHT PERCENT SR90 AND FROM ABOUT 33 TO ABOUT 65 WEIGHT PERCENT P2O5. 